Calcium silicate moldings and the recently popularized cement exterior wall materials have become essential building materials in the last few years, and are used as various types of insulating materials and as exterior wall panels for prefabricated housing and the like.
These calcium silicate moldings are prepared by dispersing lime and silicic acid in a large quantity of water and heating the resulting slurry. A crystalline structure (tobermorite, gyrolite, wollastonite, etc.) is formed that consists of a crystalline structure of calcium oxide, silicon dioxide, and water. Moldings are generally used that have been asbestos, etc.) in the slurry, pouring the slurry into a form, draining, molding, and drying or optionally steam-curing. The various types of exterior wall panels used for example, in prefabricated housing, consist of the strong, hard moldings prepared by dispersing cement, crushed silica, perlite, and asbestos to homogeneity in a large volume of water, pouring this into a form, draining, molding, and then steam-curing and drying.
At specific gravities of 0.2 to 0.5, these calcium silicate moldings have very good thermal insulating characteristics due to their high air contents. The so-called exterior wall panels typically have specific gravities within the range of 0.8 to 1.2. However, a common problem among these calcium silicate moldings has been their high water absorptiveness. For example, a calcium silicate molding immersed in water overnight will absorb about 80 to 95 weight % water. Water absorption rates of approximately 30 to 40 weight % occur even with exterior wall panels. The freezing of this absorbed water causes cracking and surface attrition, which of course is a prohibitive drawback to the application of such panels in cold-weather regions. Another problem with these materials is that their absorption of large quantities of water impairs their thermal insulating performance.
In response to these problems, there have been numerous attempts at equipping calcium silicate moldings with a native water repellency through the addition thereto of diorganopolysiloxane or a diorganopolysiloxane emulsion prepared using anionic surfactant. For example Japanese Patent Application Laid Open [Kokai] Number Sho 59-92963 [92.963/1984], Japanese Patent Publication [Kokoku] Number Hei 2-58227 [58.227/1990]. Japanese Patent Publication Number Hei 2-15511 [15.511/1990]. Japanese Patent Publication Number Hei 1-58148 [58.148/1989]. and Japanese Patent Publication Number Hei 1-35790 [35.790/1989] propose such methods.
However, these known methods suffer from several problems. When a diorganopolysiloxane is added to a large volume of water-based slurry, this diorganopolysiloxane, being insoluble in water, does not become uniformly dispersed in the slurry. This results in an uneven manifestation of the water repellency. On the other, absorption by the diorganopolysiloxane is unsatisfactory in the case of the addition of an anionic surfactant-based diorganopolysiloxane emulsion. This results in the release of diorganopolysiloxane into the waste water, which creates problems for water purification.
The present invention pertains to a method for the preparation of water-repellent hardened moldings by using an emulsion that is readily broken in the type of slurry under consideration. The emulsion may be readily broken in the type of slurry under consideration when a diorganopolysiloxane with a specific structure is emulsified using nonionic surfactant that has a cloud point and this emulsion is then mixed into the slurry at a temperature at or above this cloud point. This results in almost no release of diorganopolysiloxane into the effluent during the sheet fabrication process.
The present invention takes as its object the introduction of an efficient method for the fabrication of uniformly water-repellent hardened moldings that does not release diorganopolysiloxane into the effluent during the molding process and that provides moldings in which there is no variation in water repellency.